1. Field of the Invention
The present invention relates to an infrared ray sensor, and more particularly, to a resistive bolometer sensor in which a bridge circuit is formed on a sensor chip to reduce the production cost and a fixed resistor is replaced with a sensor resistor to reduce an error of an output value due to temperature variation, thereby sensing a temperature more exactly.
2. Background of the Related Art
Recently, sensors are widely used in various fields. As examples of the sensors for sensing infrared rays, there are a thermopile sensor based on thermal conductive effect, a pyroelectric sensor based on superconductive effect, a ferroelectric bolometer for sensing variation of dielectric ratio by applying a bias voltage to a sensor, and a resistive bolometer based on resistance variation.
Especially, the resistive bolometer has a simple fabricating process, saves the cost and facilitates control of sensitivity and noise depending on bias variation. In this respect, the resistive bolometer is used as a temperature sensor or is formed of a sensor array to be applied to an infrared ray camera.
The resistive against environmental temperature variation.
Particularly, the infrared ray sensor is being widely used, as a thermopile sensor is recently applied to a microwave oven to sense a temperature of food so that food can be heated at a desired temperature.
However, the thermopile sensor has problems that it has low sensitivity and is susceptible to a environmental temperature variation. Accordingly, a sensor having higher sensitivity and stability has been required. To meet such requirements, a bolometer sensor has been provided, which has higher sensitivity and is more stable in an abnormal state where a environmental temperature is frequently varied.
Such a resistive bolometer sensor is used to sense a temperature of an object in such a manner that a resistor is formed on a film having a small heat transfer coefficient and absorbs an infrared ray so as to sense resistance variation caused by temperature variation of a resistor.
Alternatively, to avoid variation of the sensor due to variation of a environmental temperature, another resistive bolometer sensor is configured using a bridge circuit so as not to vary a signal due to variation of a environmental temperature.
A bridge circuit of the related art resistive sensor will be described with reference to FIG. 1.
FIG. 1 shows a bridge circuit of the related art resistive sensor. The bridge circuit of the related art resistive sensor includes a sensor resistor (R1) 1 for sensing a temperature of an object, a compensation sensor resistor (R2) 2 for eliminating influence of a environmental temperature, and fixed resistors (R3, R4) 3 and 4 having a bridge structure to avoid variation of the sensor to variation of the environmental temperature.
The compensation sensor resistor 2 forms a material, which reflects an infrared ray, on a top layer.
An output value Vout of the bridge circuit is expressed by the following equation 1.                              V          out                =                              V            ref                    ⁡                      (                                                            R                  1                                                                      R                    1                                    +                                      R                    4                                                              -                                                R                  2                                                                      R                    2                                    +                                      R                    3                                                                        )                                              [                  Equation          ⁢                      xe2x80x83                    ⁢          1                ]            
The sensitivity is the highest when             R      2              R      3        =  1.
Therefore, a circuit configuration having four resistors with the same resistance values if possible significantly acts on the size of an initial zero point signal and sensitivity of the sensor. For this reason, to allow the resistors 1, 2, 3 and 4 to obtain the same resistance values, a bridge circuit is configured based on resistance values similar to the resistors 1 and 2 by considering errors of the fixed resistors 3 and 4.
However, the bridge circuit of the related resistive sensor has several problems.
Since two fixed resistors having resistance errors of 1% or greater are used, it is difficult to control the initial zero point signal and match a given resistance value produced by the process with an actual resistance value varied depending on a environmental temperature. This limits the configuration of a resistive sensor having optimal sensitivity.
Furthermore, in view of the aspect that the environmental temperature varies as units are used, the resistor of the sensor and the output of the compensation sensor vary but the two fixed resistors constituting a bridge circuit has fixed values without variation. This reduces sensitivity or causes wrong output results, thereby resulting in that the temperature is not exactly sensed.
Accordingly, the present invention is directed to a resistive bolometer sensor that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a resistive bolometer sensor in which four resistors are formed to facilitate control of an initial zero point signal and reduce a resistance error, thereby improving sensitivity.
Another object of the present invention is to provide a resistive bolometer sensor in which a fixed resistor is replaced with a sensor resistor to reduce an error of an output value due to temperature variation, thereby improving sensitivity.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a resistive bolometer sensor comprises: a sensing unit for sensing an infrared ray, the sensing unit including a sensor resistor and three compensation sensor resistors; a supporting unit for supporting the sensing unit, for controlling heat transfer to the outside; and a silicon rim supporting the overall elements of the sensor, for reflecting an external temperature, wherein the sensor resistor senses a resistance value by incident infrared ray, and the three compensation sensor resistors have a bridge structure with the sensor resistor and senses a environmental temperature to compensate a resistance value that varies in accordance with temperature variation. Furthermore, the resistive bolometer sensor is characterized in that a reflecting film is deposited on the compensation sensor resistors to reflect the infrared ray. Finally, the resistive bolometer sensor is characterized in that the sensing unit is configured in such a manner that a plurality of sensor resistors and compensation sensors are formed on one chip in a bridge structure.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.